According to the conventional wireless packet communication method in compliance with standard specifications, only one wireless channel to be used is decided in advance, whether the wireless channel is available or not is detected (carrier sense) prior to transmission of the data packet, and one data packet is transmitted only when the wireless channel is available. Such control allows one wireless channel to be shared among a plurality of stations (hereinafter, STA) by staggering times ((1) “International Standard ISO/IEC 8802-11 ANSI/IEEE Std. 802.11, 1999 edition, Information technology—Telecommunications and information exchange between systems—Local and metropolitan area networks—Specific requirements—Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) specifications”; (2) “Low-powered Data Communication System/Broadband Mobile Access Communication System (CSMA) Standard”, ARIB STD-T71 version 1.0, Association of Radio Industries and Businesses, settled in 2000).
According to the wireless packet communication method like this, the wireless packet communication method which uses the known MIMO technique (Kurosaki et al., “100 Mbit/s SDM-COFDM over MIMO Channel for Broadband Mobile Communications”, Technical Reports of the Institute of Electronics, Information and Communication Engineers, A•P2001-96, RCS2001-135 (2001-10)) to perform simultaneous transmission of the plural data packets through one wireless channel, in order to improve transmission efficiency of the data packets, is under study. This space division multiplexing technique (SDM) is the system for simultaneously transmitting the different data packets from each of plural antennas using the same wireless channel, and receiving the plural data packets which are simultaneously transmitted using the same wireless channel by digital signal processing corresponding to a difference in propagation coefficients of the respective data packets received in plural antennas of the opposing STA. The number of MIMOs is decided according to the propagation coefficient and the like.
Moreover, the wireless packet communication method in which each STA has plural wireless network interfaces and, when the multiple wireless channels are available in carrier sense, performs the simultaneous transmission of the plural data packets using the multiple wireless channels, in order to improve the transmission efficiency of the data packets, is under study.
Furthermore, the wireless packet communication method in which the number of data packets corresponding to the total number of MIMOs of the multiple wireless channels are simultaneously transmitted by combining the multiple wireless channels and the MIMO technique is also under study.
According to such methods, when there are the two available wireless channels for the three data packets, for example, the two data packets out of three are simultaneously transmitted using the two wireless channels. Further, when there are the three available wireless channels for the two data packets, all (two) of the data packets are simultaneously transmitted using the two wireless channels. This also applies to the case where the MIMO technique is used.
According to the method of performing the simultaneous transmission of the plural data packets using the multiple wireless channels, the influence of leakage power which leaks from one wireless channel to a frequency band used by the other wireless channel is significant when center frequencies of the multiple wireless channels used simultaneously are close to each other. In general, when transmitting the data packet, the transmit-side STA transmits the data packet, and thereafter, the receive-side STA returns an acknowledge packet (ACK packet, NACK packet) to the transmit-side STA in response to the received data packet. The influence of the leakage power from another wireless channel used in the simultaneous transmission presents the problem when the transmit-side STA is receiving this acknowledge packet.
For example, as shown in FIG. 23, the case is supposed that the central frequencies of a wireless channel #1 and a wireless channel #2 are close to each other and transmission times of the data packets to be transmitted simultaneously from the respective wireless channels are different. In this case, since the data packet transmitted from the wireless channel #1 is short, the wireless channel #2 is performing transmission when the ACK packet in response thereto is received. Accordingly, there is the possibility that the wireless channel #1 cannot receive the ACK packet due to the leakage power from the wireless channel #2. Under such circumstances, it is impossible to improve throughput even though the simultaneous transmission is performed using the multiple wireless channels.
Such a case is caused due to a difference in packet time lengths (transmission time=data size) of the respective data packets when transmission rates of the respective wireless channels are equal to each other, and is caused due to a difference in the packet time lengths (transmission time=data size/transmission rate) of the respective data packets when the transmission rates of the respective wireless channels are taken in account.
Further, according to a wireless LAN system, data sizes of the data frames inputted from a network are not constant. Therefore, when the inputted data frames are sequentially converted to the data packets to be transmitted, the packet time lengths (transmission times) of the respective data packets also change. Therefore, when there is the difference in the packet time lengths between the plural data packets as shown in FIG. 23, there is the high possibility that the ACK packet fails to be received even though these are transmitted in parallel simultaneously.
Relating to such problems, the method of allowing the transmission of the plural data packets to complete simultaneously or almost simultaneously by making the packet time lengths of the plural data packets to be transmitted simultaneously the same or almost the same is under study. According to this method, the transmitting station is not performing the transmission at the time when the ACK packet arrives in response to each of the plural data packets. Therefore, all the ACK packets in response to the data packets which are transmitted simultaneously can be received without being influenced by the leakage power between the wireless channels and the like, which makes it possible to contribute to the improvement of the throughput. The “simultaneous transmission” in this description refers to the state in which the plural data packets with uniform packet time length (transmission time) are transmitted simultaneously. This also applies to the case of the MIMO transmission.
Now, there are the following three ways of generating the plural data packets to be transmitted simultaneously from the data frames. When the data frame is one and the number of idle channels is two, for example, the two data packets having the same packet time length are generated by fragmenting the data frame as shown in FIG. 24(1). Further, when the data frames are three and the number of idle channels is two, the two data packets having the same packet time length are generated by dividing a data frame 2, for example, and connecting these to a data frame 1 and a data frame 3, respectively, as shown in FIG. 24(2). Alternatively, it is the same when the three data frames are connected and then divided into two. Further, as shown in FIG. 24(3), the data frame 1 and the data frame 2 are aggregated and dummy bits are added to the data frame 3, to generate the two data packets having the same packet time length. When the transmission rates of the respective wireless channels are different in using the multiple wireless channels, adjustment is made by bringing size ratio of the respective data packets into correspondence with transmission rate ratio so that the packet time lengths become the same.
Further, according to the wireless LAN system, one data frame is converted to one MAC (Media Access Control) frame. Therefore, even when the data size of a data field in the data frame is small, it is converted to one MAC frame and transmitted as one data packet (for wireless transmission). For example, the maximum size of the data field in the MAC frame of IEEE802.11 standard is 2296 bytes, whereas, in an Ethernet (Trademark) frame which is used as the data frame in general, the data size of the data field is limited to 1500 bytes at the maximum. Accordingly, the Ethernet frame having the maximum size has a margin with respect to the maximum size (2296 bytes) of the data field in the MAC frame. Namely, according to the conventional system, the maximum data size which can be transmitted by one MAC frame is not utilized efficiently, and there is the limit to the improvement of the throughput.
Therefore, in order to utilize the data size of the data packet to the greatest extent possible, the method of aggregating the data fields of the plural data frames and transmitting these as one data packet, as shown in FIG. 24(4), is also under study. In the methods shown in FIG. 24(1) to (3), the connection of the data frames and the like is performed in the range of the maximum size of the MAC frame.
Now, it is possible to deal with the plural data packets generated by the division of the frame as shown in FIG. 24(1) according to the frame format in compliance with the standard specifications based on the conventional fragment processing. Meanwhile, the data packets which are reconstructed by patching the data frames as shown in FIG. 24(2) and aggregating the data frames as shown in FIGS. 24(3) and (4) are in a special format which is not in compliance with the standard specifications.
However, it is needless to say that, in such a data packet in the special format, the data field of the data frame and the data field of the data packet are not in one-to-one correspondence. Meanwhile, the receive-side STA needs to restore the original data frames from the received data packet, but the restoration from the as-is data packet is not possible because its packet format is unexpected conventionally. The reasons are as follows.
When an IP packet in an IP layer is transferred to a lower layer in the actual system, for example, the processing of transferring it is performed by fragmenting it into several data frames. In this case, headers for restoring the original IP packet are respectively added to head parts of the data fields of the respective data frames formed by the fragmentation. When a receive-side STA receives the data packets formed by thus-generated data frames, it extracts the data frames from the data packets, and then restores the original IP packet.
Generally, in the IP layer of the receive-side STA, restoring processing on the IP packet is performed by automatically recognizing that the head part of the data field of each of the received data frames is header information necessary to restore the original IP packet. Namely, from the viewpoint of the IP layer, the problem is caused when the head part of the data field in each data frame is not the header information to restore the original IP packet.
However, in the data packet which is reconstructed by patching or aggregating on the transmit side as described above, the header information to restore the original IP packet is moved to the part other than the head of the data field in each data frame, and therefore the IP packet cannot be restored from the as-is data packet in the IP layer. Therefore, before restoring the IP packet, it is necessary for the receive-side STA to first restore from the received data packet the original data frames before the reconstruction.
In order for receive-side STA to restore the data frames before the reconstruction from the data packet in the special format which is reconstructed on the transmit side, information on whether the data packet is in the special format or not, and when it is in the special format, information such as the boundary of the data frames and the order of the data packets are necessary. However, since a field for transmitting such information is not defined in a standard format, it is necessary to transmit the information from the transmit side to the receive side by the special format which is newly defined. However, when the special format which is not defined generally is adopted by the entire communication system, all the STAs which constitute the communication system must be replaced by new devices supporting the special format, and therefore increase in cost is unavoidable.
It is an object of the present invention to realize the wireless packet communication method which enables transmission/reception of the data packet in the special format, recognizing that it is in the special format, and the restoring processing on the data frame before the reconstruction in the wireless packet communication method in which the data packet in the standard format is transmitted/received.